The present invention relates to generation indicating apparatus for vehicle alternators and more particularly to a generation indicating apparatus having a function of protecting a indicator lamp drive circuit.
Transistorized generation indicating apparatus are generally known in the art and this type of apparatus is designed so that an indicator lamp is turned on during the time interval between the closing of a key switch and the time that the generated voltage of an alternator reaches a predetermined value, thus indicating that the alternator is not generating. On the other hand, if an abnormal voltage is applied to the terminal (hereinafter referred to an L terminal) between the indicator lamp and the output end of a circuit for driving the indicator lamp due to short-circuiting of the indicator lamp, contact failure of the "L" terminal with a power supply circuit or the like causing erroneous application of the voltage from the power source or the L terminal being directly connected to the ground terminal, there is the danger of breaking a circuit element of a generation indicating circuit such as a transistor. Generation indicating circuits of the type having a protecting circuit for preventing such trouble have been proposed.
This type of protective circuit is so designed that the voltage at the L terminal is detected such that when the voltage at the "L" terminal becomes abnormal and exceeds a predetermined value during the indicating operation (where the alternator is not generating power and the indicator lamp is turned on) or the voltage at the L terminal becomes abnormal and lower than the predetermined value under the electric load driving condition (where the engine has started so that the alternator is generating an output voltage higher than a predetermined value and the indicator lamp is off), the indicating operation or the load driving is stopped and breaking of the transistor in the drive circuit is prevented. However, this type of protective circuit is disadvantageous in that it has no resetting function so that once an abnormal voltage has been detected and the generation indicating or load driving operation as been stopped, even if the abnormal voltage is eliminated and the normal condition is restored, it is not always possible to bring back to the former or normal operating condition.